The present invention relates to fluid controllers of the type used to control the flow of fluid from a source of pressurized fluid to a fluid pressure actuated device, such as a steering cylinder.
Although the present invention may be used with fluid controllers of many types, and having various constructions and applications, it is especially advantageous when used with a full-fluid-linked steering controller, for use on a vehicle of primarily the “off highway” type. Therefore, the present invention will be described in connection therewith.
A typical prior art fluid controller and valving therefor is illustrated in U.S. Pat. No. 4,620,416, assigned to the assignee of the present invention and incorporated herein by reference. The typical prior art fluid controller of the type to which the present invention relates includes a housing which defines various fluid ports, and further includes a fluid meter, a valve means defining a main fluid path, and an arrangement for imparting follow-up movement to the valve means, in response to the flow of fluid through the fluid meter.
In the typical prior art fluid controller, all flow to the fluid pressure actuated device must first pass through the fluid meter. Thus, the typical prior art fluid controller requires a relatively large displacement fluid meter when used in large “off highway” vehicles. However, the use of large displacement fluid meters in the fluid controller adds substantially to the size and cost of the controller.
U.S. Pat. No. 4,759,182, assigned to the assignee of the present invention and incorporated herein by reference, addressed the above-described size and cost concerns by disclosing a fluid controller with the capability of providing flow, to the fluid pressure actuated device, wherein the flow to the device (steering cylinder) is substantially larger than the flow through the fluid meter of the controller. While the fluid controller of the '182 patent continues to be a commercially successful product used in many hydraulic applications, the overall stability of a steering system using such a “flow amplification” controller decreases, in some instances, when the ratio of the total flow to the flow through the fluid meter is substantially larger than about 2:1